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  <a href="http://sudopedia.enjoysudoku.com/Bivalue_Universal_Grave.html">BUG+3 (with Naked {4})</a>
  <p>
  	If the <b>candidates {0}</b> were removed from the highlighted <b>cells {1}</b> each unsolved cell would have two candidates and each candidate would occur exactly twice in each row, column and block.<br/>
  	A Sudoku showing this so-called BUG (Bivalue Universal Grave) has either zero or two solutions rendering the puzzle invalid.<br/>
    Extra candidates in one of the unsolved cells are needed to avoid this <a href="http://sudopedia.enjoysudoku.com/Deadly_Pattern.html">deadly pattern</a>. 
  </p> 
  <p>
  	The highlighted <b>{1}</b> are the only cells with extra candidates: <b>{0}</b>.<br/>
	To avoid the deadly pattern at least one of these cells must contain the <b>value {3}</b>.<br/>
	Consequently one of the <b>cells {1}</b> forms a Naked {4} with <b>{5}</b> for the <b>values {6}</b> in the highlighted <b>{7}</b>.<br/>
	All other occurences of the <b>candidates {6}</b> in <b>{7}</b> can therefore be removed.
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